Apparatus for separating dust from gas, particularly hot gas



Feb. 16 1960 w, o, KRQLL 2,925,144

APPARATUS FOR SEPARATING DUST FROM GAS, PARTICULARLY HOT GAS 5Sheets-Sheet 1 Filed Feb. 7, 1956 IN VE NTOR.

a! aw/M Feb. 16, 1960 w. o. H. KROLL 2,925,144

APPARATUS FOR SEPARATING DUST FROM GAS, PARTICULARLY HOT GAS Filed Feb.7, 1956 3 Sheets-Sheet 2 INVENTOR.

W 012; [M (M Feb. 16, 1960 w. o. H. KROLL.

APPARATUS FOR SEPARATING DUST FROM GAS, PARTICULARLY HOT GAS Filed Feb.7, 1956 3 Sheets-Sheet 3 INVENTOR.

ctimpletely upon these'bo'dies;

United States Patent $925,144- APPARA'EUSFGK Shin jiUS'l i i'z'oM GASPARTICULARLY HOT GAS wen-a Otto fiat-ale Kain, Koln-Deu'ti, ce miany,as-

signor toIQiickner-Hu'rnboldt-Deutz Aktienge'sellsehaft,

Koln-Deutz, Germany, a corporation of Germany Application mam-y 7, 1956,Serial No. 564,679 Claims'p'riority, application Germany Feliruary9,1955

s Claims. class- 52 My invention relates to separators for removing dustfrom gas and has for its main object to devise a dust filteringapparatus which is insensitive to high temperatures .and combines simplemechanical construction with good separating efficiency and particularcase of cleaning.

To this end, and in accordance with a feature of my invention, 1 providea housing with respective connectionsfor the supply of dust-laden, gasand the discharge of clean gas, :and ,I- dispose in the housing amultitude of elongatedfilte'r elements, such as wires, strips or rods ofmaterial, in spaced relation to one another. The

elements are distributed over the entire cross section of the housingandare located inseveral planes likewise spaced from one another,:Lfurther provide the assembly of wii'e- :.or rod-shaped filter; bodieswith devicesisrfor instance strippersor' scrapers, for removing thecollected .dust adheringto the'filter bodies. In the following de-.s'cription the filter bodies, regardless of their particular shape orsize, .are'briefiyreferred to as wires.

The invention is based uponthe recognition that dust particles willdeposit' themselves-upon the surface of a body impinged upon byajfiow ofdust-laden gas. This occurs to a g'reaterwdegree the higher the velocityof the gas flow; The reasonfor this phenomenon resides in the factthatat high gas velocities the inertia of the dustparticlesto changes inflow direction is so large that whereinv is the' sink ing-veloci ty of adust particle in stationary air, V the gastvelocity, g the gravityacceleration, andjD the: diameter of the separator body.

In apparatus according to the invention the dustladen gas, on itspaththrough the housing, impinges --upon the wires;

Each, individual wire thus represents a body located within the gasstream as explained above. Therefore, if i the gasgvelocity is chosencorrespondingly high and if a sufficient numberof wires or rods areprovided, the" dust can be caused to precipitate virtually Since thewires are provided with-devices for removing the precipitated dusttherefrom, the periodically required cleaningof' the filtering apparatusis very simple.

The foregoing and more specific objects, advantages and features of theinvention, such features being defined with particularity in the claimsannexed hereto, willbe apparent from the two embodiments illustrated byway of example on the accompanying drawings in which:

Fig. 1 shows a filteringapparatus partiallyin cross sections apartialkcrosjssection taken" along the line y 2,925,144 Patented Feb.16, 1969 Fig. '3' is a' section taken along the line III-III in .alOngthe line VII--VII in Fig'. 6.

Fig; 8 shows in longitudinal section an apparatus for separating dustfrom gas with two filters in which the wires are mounted ,sta'tionarily;Fig. 9 is a cross section along the line IX-IX in Fig 8; and

Fig. 10 -is .a cross" section along the line X--X in Fig. 9;

The filter according to Fig; 1 has a sheet-metal housing 1 ofrectangular cross section. The housing hasab'ottorn: duct 2 forthesupply of hot dust-laden air from-a'supply conduit 3. .The' top ofhousing 1 is providedxwith a connecting duct 4 for the discharge of thedust-free gas. Duct 4 is joined with the suction inlet of a blower 5whose pressure outlet communicates with the open air through a conduit6. A large number of wires 7 .of circular cross section extend throughthe housing 1 in parallel relation to the narrowwalls 8 and 9 of thehousing; The wires 7 are spaced from each otherand are uni'formlydistributed .over the entire cross section: as theihousing and disposedin a number of different planes. Although for'simplicity, only threearrays ofwire's' inplanes 10,11,12 are shown on the drawin'g a largernumber of such arrays or planes is generallylneeded, and five to fiftyormore such arrays dividual-wiresiis in the range between about 0.5 to 20mm: and is preferably made larger with increasing coarseness of the-dustto be separated. Thes'pacing a (Fig. 5) between each two adjacent wireswithin the same-pla'neis' preferably made equal or somewhat larger thanthe wire diameter, and the spacing b (Fig. 2) between two adjacentplanes is preferably made a multiple of, for instance three timesaslarge as, the diameter. It is further preferable to" arrange, thewiresso that the wires in one plane are displaced relative to the Wires ofthe neighboring planes by one-half of the spacing a. The wires 7 pass'through holes 13 in the longitudinal walls 14 and 15 of the housing 1with sufiicient clearance to be readily displaceable' in thelongitudinal direction of the wires. The drawing (Figs. 1-, 3) shows thewire assembly in its right-hand position. As illustrated, the wireassemblies have such a length that theportion c (Fig. 3) projecting outof the filter space in the housing is somewhat longer than the portion dlocated within the housing 1. Preferably, and as shown, the wires 7 havetheir ends attached to respective transverse bars 16; 17 of a framestructure 35 whose longitudinal bars 18 and19 are displaceably mountedin lateral guides 20, 21 of housing 1. Mounted'within the housing 1 arewalls 22, 23 which, together with the longitudinal and transverse wallsof housing 1, enclose lateral spaces 24 and 25. The top of eachpartition wall 22, 23 is curved toward engagement with the longitudinalwalls of housing 1 thus upwardly closing'the spaces 24 and 25. Thebottoms of spaces 24 and 25 form respective connecting ducts26 and 27for discharging the dust into respective dust outlet pipes 23 and 29.

A valve 36 or 31 is preferably mounted within each of dust dischargepipes 28 and 29 and is loaded or weighted in the closing sense. Thepartitions 22, 23 are provided a with holes 32 for the passage of thewires 7. The holes 3 made so large as to offer ample clearance to thewires especially in the downward direction. Instead of providing a rowof holes 32 according to Fig. 5, each partition may also be providedwith a single slot of corresponding Width extending horizontally overthe entire length of each array of wires of a single plane.

During operation of the filter apparatus, the blower 5 operates to forcedust-laden hot gas, for instance exit gas from a heating device forcement raw material, from gas supply conduit 3 through housing 1. On itspath through the ho'using the gas impinges upon, and flows around, theseWires. With a sufficiently high velocity of the gas flow; the entraineddust precipitates in the manner described aboveontothe lower side of theWires impinged upon by the gas. The gas thus liberated from the dustpasses subsequently through the components 4, 5 and 6 into the ambientair. In time, the dust deposits itself upon the wires as shown in Fig.5; As is apparent, the

gaps between the individual wires remain fully open during normaloperation. Thus the gaps are always available without hindrance for thepassage of the gas.

mounted as described with reference to the illustrated em- -'bodiments,the wires may also be stationarily mounted Hence, the resistance to'theflow of gas through the housing remains substantially constant and doesnot appreciably increase due to deposition of dust as is the case withother mechanical filters.

As explained above, the velocity of the gas guided toa very good dustseparation is obtained with. a gas velocity of 7 meters per second..With dusts of the just mentioned grain size, a diameter of the wires ofapproxi 'mately 3 'mrn. is well suitable The operating condition reachedaccording to Fig..- 5

' is such that the wires are so much occupied by dust that a furtherincrease in dust deposition would impair the separating operation. Ifthis condition is reached, the

position in which the cross bar 17 abuts against the longitudinal wall15 of the housing 1 and the portion c of the wires' is located in theinterior of the housing. Now

a clean portion of the wires is available for the separation of dustfrom gas. During displacement of the frame 35 the dust carrying portionsd of the wires 7 are cleaned simultaneously. The cleaning operation isapparent from Fig. 4. It will be recognized that the holes 32 inpartition 22 are so large that not only the wires 7 but also theadhering dust can freely pass through. In

contrast, the holes 13 in the longitudinal wall 14 are only as large asis needed for the passage of the wires, but they are not large enoughfor passage of dust. As a result, the dust is scraped off as the wirespass through partition wall 22. The dust drops through space 24 andcollects upon the valve 30 (Fig. l). The closing moment ward the filterwires depends upon the grain size of the dust and is made larger with afiner grain size. For instance, if the dust has a medium grain size of 3microns,

'frame 35 with wires 7 is displaced into the left-hand limit tion sothat the above-described cleaning operatio'n willv again occuranalogously. Consequently thefilter apparatus hasalso the advantage thatthe dust separating operation remains continuous rather than beinginterrupted by the periodically required cleaning of the filter wires.

The filter apparatus illustrated in Fig. 6 is particularly designed forthe removal of dust from gas which carries dust of very fine grain sizeand consequently must be blown against the Wires at a very highvelocity.. As shown, the Wires 40 of the filter are arranged in thenarrowest cross section of a nozzle-shaped housing 41. Such a shape ofthe filter housing makes it possible to economically attain very highgas velocities. Also with reference to the very high gas velo'city, thewires 40 are preferably the scraper plate.

given a streamlined cross section as shown in Fig. 7. Such wires offerto the gas. flow a considerably smaller resistance than, for instance,those of circular cross section. According to Fig. 6 the wires of eachplane or array are mounted in an individual frame 42. Each individualframe can readily be displaced by hand. However, as in the embodiment inFigs. 1 to 5, all wires-may also be mounted in a common frame. Then thedisplacement of the frame is preferably effected by means of a motorwhich, for instance, may drive a pinion'meshing with a rack on the framestructure.

The filter according to Fig. 6 further differs from the one describedpreviously in that gaskets or seals 43, for instance of asbestos, areprovided at the places where the wires 40 emerge out of the housing 41.g This alfords the assurance that at these places no air is'inductedfrom the outside into the housing. Of course, such sealing means mayalso be provided in filter apparatus otherwise according to Figs. l'to5.

* Whilewe prefer having the filter wires displaceably such' filters arerequired. 7 They are connected to a common supply-conduit 54 for thedust-laden gas and also to a common discharge conduit for the-dischargeof the clean gas. Besidesythe apparatus is provided with flap valves sothat the' gas can-be selectively passed either :through the one orthrough the other filter. When the wires ofthe filter first traversedby'thegas are so greatly loaded with separated'dustas to requirecleaning, then this filter is switched from the supply and dischargeconduits for the gas by correspondingly turning the valve flaps; andinstead the other filter is placed in operation. The filter wires of thefirst filter are cleaned by displacing The dust scraped off the wiresthen drops through the housing and is collected in a pocket located atthe bottom of the filter. Subsequently the collected dust can be removedfrom the pocket. Thereafter the filter first used is again ready foroperation. When after a certain time the wires of the second-used filterrequire cleaning, then they are separated by means of the valve flapsfrom the supply and discharge conduits for the gas, and thefirst-mentioned filter is again placed into operation. The cleaning ofthe second filter is then performed in analogy to the cleaning operationdescribed above.

In a filter according to the invention the Wires of the planes or arraysfirst impinged upon by the gas are most strongly occupied by separateddust. Consequently, the wires of the subsequent planes are still capableof receiving dust when the wires of the forward plane or planes mustalready be cleaned. For that reason it is preferable to give the wiresin the forward planes a larger cross section than, for instance twicethe cross section of, the wires in the subsequent planes, the latterwires having their cross section dimensioned in dependence upon thegrain size of the dustto be. separated. Obviously, when the streamlinedbaffles or wires of Figure 7 are employed, the transverse thickness isthe dimension that'is determined in dependenceupon thegrain size. Whenbaffles or wires'of circularcross-section are used the criterion is thediameter, or the cross-sectional area, which is proportional to thediameter. wires' can receive more dust than thinner ones, care istaken-'in this matter that all wires are utilized to an approximatelyuniform extent so as to require approximately the same period ofoperation before they become thick wires, spaced from each other adistance-ahputequal Since thicker rearward planes.

:gas from the common supply conduit 54.

to t heir diameter otter-to" the. passage. of gas a lesser resistancethan" thiii wires likewise spaced from each other a distancecorrespondingto theirQdiarneter. Ob- I iously, this appliesto bothcircular and streamlined {Barnes Consequently, a filter whose wire-sarefall diri'lension'e'cl in accordance with the grain size of thedu'stt obe separated involves morepre'ssure losses than a filter which theforward filter planes are occupied. by wires thicker thanreguired.Furthermore, the thicker wires of the forward planes recei-vemainly theprecipitation of coarser dust particles whereas the finer particlesprecipitate to a larger extent onto the thinner Wires of the Theprovision of thicker wires in the forward planes as compared with thewires in the subsequent planes is therefore also of advantage in caseswhere the gas entrains dust particles of greatly different grain sizes.

Since, as mentioned, more of the coarser dust particles adhere, to,thewires of the, forward planes and more finer partlcles on the wiresofthe rearward, and since further for theseparation of the coarserparticles alower gas velocity isneeded than for the separation of thefiner particles, it-is further of advantage to pass the gas through thefilter at a velocity increasing from the forward toward the rear planes.Such increase in gas velocity can be obtained readily, for instance'in afilter according to Figs. 1 to 5, by having the cross section of thehousing 1 decrease continuously from the lower toward the upper planeofth'e assembly of filter wires.

-In further relation to Fig. 8, each of the two filters of thisapparatus has a housing 50 and 51 of rectangular cross section; Thebottom .portion of each housing forms aconnecting duct 52, 53 for thesupply of dust-laden The top portion of each housing forms a connectingduct 55, 56,

.through which the cleaned gasis discharged into a com- -mon outletconduit 57. Conduit 57 communicates with the? suction side of a blower58, whose pressure outlet communicates with the open air through aconduit 59. Each ofthe ducts 52 and 53 is provided respectively with .apocket 60, .61. The bottom portion of each pocket is provided with adischarge pipe 62, 63. A rotary valve 64, 65 is mounted within-each of:the pipes. At the edges 661.671 where the ducts 52, 53 and 55, 56 of thetwo housings arenjoined with each other valve flaps 68, 69 are provided.The flaps are interconnected (not shown) so that they can be placedsimultaneously from the outside-by aid of a hand lever 70 into the fullline or the Inside eachhousing a large number of wires 74,75 isprovided; At their ends the wires are firmly connected With the walls ofthe housings. For cleaning the wires in each housing a movable scraper76, 77 is disposed. Itconsistsof a plate with holes 78 (Fig. 10). Eachwire passeswith clearance through a hole of the plate. Furthermore a rod80, 81 which passesthrough the housingris fastened to each scraper. Byaid of the rods the scrapers can be moved to and fro on the wires.

- During operation of the apparatus the flaps are in the full linepositions or in the dot-and dash line positions,

so that the dustladen gas passes through one of the two filters. Withsufficient high velocity of the gas flow, the entrained dustprecipitates as described onthe wires of this-filter. When the wires areso greatly loaded with separated dust as to require cleaning, then theflaps are turn ed,*so that the other filter is placed in operationwhereas the first filter is separated fron the gas conduits 54,,57.Thereafter the scraper 76 of this filteris moved tognd fro by the rod80. By this the dust is scraped pt ffrprn the wires and drops into thepockets 60. Subable for dust removin'g'ope'ration;

1. Apparatus for the mechanical cleaningof dust lade'n gas, comprisingaihotis'ingjh viii "rijiriletportionlfor dust-laden gas and an outlet"onfor cleaned gas, said housing having between said two portions a zoneof a narrower cross sectionlthan saidp tions so asflto form a nozzlestructure together withrsaidportions; filter means disposed in said zoneof said h'ousiri'g' and comprising arrays of parallel free s'paced fromeach other within each saidarray anddistributedjover the cross sectionof said housing re, said arrays being located in different respectiveplanes" spaced fronijeach other between saidinlet and o ltl tpbrtions;and scraper means mechanically engage'able with; said respective wiresfor removing adhering dusttherefromisaid wiresbe'ing free of each otherlaterally toprovide'jfree' access thereabout of the scraper means. t g p2. Apparatus for the mechanicalclefaning of dust-laden gas, particularlyhot gas, which comprises a housing having an inlet portionfordiist-la'defi gasa'nd an outlet porthe elements of thatplaneithezspacing' between adjacent planes being a multiplefof thetransverse thickness of the elements of said adjacent planes, theelements'f adjacent arrays being transversely displaced, the saidthickness of the elementsdecreasiiig" in the flow direction, cleaningmeans having s ructure mechanically engageable with the periphery of andalong'the length of each element, said ra e-cav rns: and cleaning meansbeing movable relative to each other forrr'novin'g adhering dust fromsaid elements, said bathe elementsbeirig free of' each othertransversely tbp'roitide free access thereabout of the cleaning means.

3. In gas cleaning apparatus according to claim 2, said bafiles havingan air-foil cross section tapering in the gas flow direction. v

4. Apparatus according'to claim 2, comprising a rigid frame structure onwhich said arrays ofbafilles are mounted, said frame being slidablyguided on said housing for simultaneous displacement of said arrays.

5. Apparatus acc'brding'to claim 2, comprising a plurality of rigidframe structures individually guided on said housing for horizontaldisplacement relative thereto, each said arrays of bafiiesbein'g mountedon one of said respective frame structures.

6. Apparatus for the mechanical cleaning of dust-laden gas, particularlyhot gas, which comprises a housing having an inlet portion fordust-laden gasand an outletportion for cleaned gas, filter rriean'stransversely disposed within said housing and corisistiiig of arrays ofparallel free wires spaced from each otherwithin' each array andtransversely distributed over' the cro'ss section of said housing, saidarrays being'rriountecl" in at least five respectively different planespaced from each other between said inlet and outletpoiftioris', thespacing between the wires Within each plane banger least equal to thetransverse thickness of the'wii'esof that plane,-the spacing betweenadjacent planes" being" ajrnultiple of the transverse thickness of thewires of said adjalc'ent planes, the wires of adjacent arrays heing'transversely displaced with respect to each other, the said thicknessesof the respective wires decreasing in thefloiiv direction, cleaningmeans having structure mechanically e'ngageable with the circumferenceof arid alongthe lngth. ofeach-wire, one of said respective filter andcleaning means being movable relative'to the other for removing adheringdust from said wires, said wires being free of each other portions a gascleaning zone, ai'rays of elongated baflles located in said zonetransversely of the housing in mutually spaced horizontal planes, thebaffles of each array being mutually spaced and parallel and beingdistributed over the cross section of said zone, said arrays beingd-isplaceable into andjoutof the' gas cleaning zone in a directiontransversely, of said housing and having in said direction a totallength at least twice the length of the array portion located withinsaid cross section of said housing zone, the latter portion beingentirely displaceable out of said gas cleaning zonein oppositetransverse directions, and means provided by said structure outside ofand 'at opposite sides of the gas cleaning zone,

V and juxtaposed with respect to the portions of the baflles displacedoutside of the gas cleaning zone, to contact and to remove the dust fromthe baflles as they are so displaced in said opposite transversedirections, said baffles being free of each other transversely toprovide free access thereabout of the contact means.

8. Apparatus for cleaning dust-laden gas, comprising a vertical housingstructure providing a housing having an inlet portion for dust-laden gasand an outlet portion for cleaned gas, said housing having between saidtwo portions a gas cleaning zone, arrays of elongated baffies located'insaid zone transversely of the housing in mutually spaced horizontalplanes, the baffies of each array being mutually spaced and parallel andbeing distributed 'over the cross section of said zone, said arraysbeingdisplaceable in and out of. said housing in opposite directionstransversely of said housing and having a total transverse lengthatleast twice the length of the'array portion located within said crosssection of said housing zone, the latter portion beingentirelydisplaceable into and out of said gas cleaning zone in oppositetransverse directions, and means provided by said structure at oppositesides thereof to scrape the dust from the bafiles as they are sodisplaced, each of said means providing scraping apertures through whichindividual bafiles pass, said bafiles being free of each othertransversely to provide free access thereabout of the scrapingapertures.

9. Apparatus for cleaning dust'laden gas, comprising a vertical housingstructure providing a housing having an inlet portion for dust-laden gasand an outlet portion for cleaned gas, said housing having between saidtwo portions a gas cleaning zone, arrays of elongated baffles located insaid zone transversely of the. housing in mutually spaced horizontalplanes, the baffles of each array being mutually spaced and parallel andbeing distributed over the cross section of said zone, said arrays beingdisplaceable in and out of said housing in opposite directionstransversely of said housing and having a total transverse length atleast twice the length of the array portion located within said crosssection of said housing zone, the latter portion being entirelydisplaceable 7 into and out of said gas cleaning zone in oppositetransverse directions, and means provided by said structure at oppositesides thereof to scrape the dust from the bafiles as they are sodisplaced, each of said means providing scraping apertures through whichindividual bafiles pass, said baflles being free of each othertransversely to provide'free access thereabout of the scraping aperturesand two'opposite vertical apertured partitions within the housing andseparatingthe gas cleaning zone from the respective means providingscraping apertures, the apertures of ijsaid partitions providingclearance for passage of the dust on said baffies, said partitionsforming conduits to receive the dust scraped off the bafiles by saidmeans providing scraping apertures, and dust'discharge ducts extendingfrom said conduits to the outside of thehousing.

10.'Apparatus for the mechanical cleaning of dustladen gas, particularlyhot gas, whichv comprises a housing having an inlet portion fordust-laden gas and an outlet portion for cleaned gas, filter meanstransversely disposed .within said housing and consisting of arrays ofelongated parallel baffle elements of curved outline spaced from eachother within each array and transversely distributed over the entirecross section of said housing, said arrays being mounted in at leastfive respectively different planes spaced from each other between saidinlet andoutlet portions,

the spacing between the elements within each plane being at least equalto the transverse thickness of the elements of that plane, the spacingbetween adjacent planes being .a multiple of the transverse thickness ofthe elements of vsaid adjacent planes, the elements of adjacent arraysbeiri'g transversely displaced, the said thicknesses of the respectiveelements decreasing in the flow direction, said arrays beingdisplaceable in and out of said housing in opposite directionstransversely of said. housing and having a total transverse length atleast twice the length of the array portion located within said crosssection of said housing zone, the latter portion being entirelydisplaceable into and out of said gas cleaning zone, in oppositetransverse directions, and means provided by said structure at oppositesides thereof to scrape the dust from the baflles as they are sodisplaced, each of said means providing scraping apertures through'whichindividual baffles pass, said baffles being free of each othertransversely to provide free access thereabout of the scrapingapertures,

11. Apparatus for the mechanical cleaning of dust vladen gas,particularly hot gas, which comprises a housing having an'inlet portionfor dust-laden gas and an outlet portion for cleaned gas, filter meanstransversely disposed within said housing and consisting of arrays ofelongated parallel battle elements of curved outline spaced from eachotherwithin each array and transversely distributedover the entire crosssection of said housing, said arrays being mounted in at least fiverespectively different planes spaced from each other between said inletand outlet portions, the spacing between the elements Within each planebeing at least equal to the transverse thicknesses of the elements ofthat plane, the spacing between adjacent planes being a multiple of thetransverse thicknesses of the elements'of said adjacent planes, theelements of adjacents arrays being transversely displaced, the saidthicknesses of the respective elements decreasing in the flow direction,said arrays being displaceable in and out of said housingin oppositedirections transversely of said housing and having a total transverselength at least twice the length of the array portion located withinsaid cross section of said housing zone, the latter portion beingentirely displaceable into and out of said gas cleaning zonein oppositetransverse directions, and means provided by said structure at oppositesides thereof to scrape the dust from the battles as they are sodisplaced, each of said means providing scraping apertures through whichindividual bafiles pass, said bafiles being free of each othertransversely to provide free access thereabout of the scrapingapertures, and two opposite vertical apertured partitions within thehousing and separating the gas cleaning zone from the respective meansproviding scraping apertures, the apertures of said partitions providingclearance for passage of the dust on said bafiles, said partitionsforming conduits to receive the dust scraped off the bafiies by saidmeans providing scraping apertures, and dust discharge ducts extendingfrom said conduits to the outside of the housing.

12. The apparatus defined in claim 2 in which 'the diameter of thebafiie elements in the entranceplane is a elements is narrower thanthegas inlet portion leading to said housing section, to facilitateobtaining high velocities in the latter, the baflle elements beingstream-lined.

14. The apparatus defined in claim 2, in which the cross-section of thehousing section containing the baflle elements is narrower than the gasinlet portion leading to said housing section, to facilitate obtaininghigh velocities in the latter.

15. Apparatus for the mechanical cleaning of dust-laden gas, comprisinga housing having an inlet portion for dust laden gas and an outletportion for cleaned gas, said housing having between said two portions azone of a narrower cross section than said portions so as to form anozzle structure together with said portions, filter means disposed insaid zone of said housing and comprising arrays of parallel free wiresspaced from each other within said array and distributed over the crosssection of said housing zone, said arrays being located in differentrespective planes spaced from each other between said inlet and outletportions, and scraper means mechanically References Cited in the file ofthis patent UNITED STATES PATENTS 858,607 Krautzberger July 2, 19071,436,569 Boerum Nov. 21, 1922 1,484,260 Gibbs Feb. 19, 1924 1,582,499Zopf Apr. 27, 1926 1,632,813 Wittemeier June 21, 1927 2,630,878 Hopperet a1 Mar. 10, 1953 FOREIGN PATENTS 10,029 Great Britain Nov. 23, 1911190,550 Great Britain Dec. 27, 1922 746,886 Germany Aug. 28, 1944

